(a) Field of the Invention
The present invention relates to novel disazo compounds, a process for the preparation of the same, and application of said disazo compounds and analogues thereof to electrophotographic sensitive materials.
(b) Description of the Prior Art
It is known that some organic compounds, for instance, indigo-type compounds, phthalocyanine-type compounds, etc., are useful as a photoconductive material for preparing photosensitive materials for use in the electrophotographic process. The "electrophotographic process" herein is one of the image-forming processes which generally comprise first charging a photoconductive sensitive material with electricity by corona discharge or the like in the dark, subsequently subjecting it to image-wise exposure so as to discharge the electric charge of the exposed area selectively, thereby obtaining an electrostatic latent image, and then rendering visible this latent image area by a developing means employing a toner, etc., thereby forming an intended image. As the fundamental characteristics required for the photosensitive materials for use in the electrophotographic process, there are enumerated (1) an appropriate chargeability in the dark, (2) a low dischargeability in the dark, and (3) a rapid dischargeability with exposure to light. As a matter of fact, however, the known organic photoconductive compounds have not always sufficiently satisfied these requirements.
As applicable photoconductive materials, there are known inorganic materials such as selenium, zinc oxide, etc., of which selenium has admittedly been widely put to practical use. However, with the adoption of various electrophotographic processes, there is an increasing demand for, for instance, a belt-shaped photosensitive material or the like having the aforementioned fundamental characteristics as well as a satisfactory flexibility with respect to the shape thereof. In this regard, the foregoing selenium is generally difficult to form into a photosensitive material having such a shape as above.
Meanwhile, as the electrophotographic sensitive material prepared by forming a photosensitive layer containing some azo compound, as an effective ingredient, on a conductive support, such one as prepared by employing monoazo compound (cf. Japanese Patent Publication No. 16474/1969), one prepared by employing benzidine-type disazo compound (cf. U.S. Pat. No. 3,898,048, U.S. Pat. No. 4,052,210), etc. are well known. These azo compounds are admittedly useful materials as an effective ingredient of the photosensitive layer as stated above, but when various requirements for photosensitive materials are taken into account from the viewpoint of the electrophotographic process, there has in fact not yet been obtained such a material as will sufficiently meet these requirements. Therefore, it is a matter of more importance to provide a wide variety of compounds, not limiting to azo compounds, so as to afford a wide range of selection of compounds acting as an effective ingredient, thereby rendering it possible to provide a photosensitive material apposite to any specific process. In other words, it is desirable for the electrophotographic process that the variety of the compounds useful as an effective ingredient of photosensitive materials is as wide as possible.